In Situ Photochemical Activation Of Sulfate For Degradation Of Triclosan And M-cresol In Water

Triclosan and m-cresol are two endocrine disruptors existing in water.Triclosan may produce dioxins and other substances under the action of light,heat and microorganisms,and react with chlorine in water to produce chloroform.M-cresol can interfere with the endocrine system of organisms and has strong corrosiveness.Therefore,it is necessary to study the removal of triclosan and m-cresol in water.Considering that the in-situ photochemical activation of sulfate radical does not need additional oxidant,it only uses sulfate radical existing in water to activate,which is green and environmentally friendly.In this paper,in situ photochemistry activated sulfate was used to degrade endocrine disruptors in water.Two endocrine disruptors triclosan and m-cresol were selected as target pollutants.The effects of BiPO₄ dosage,Na₂SO₄ concentration,initial concentration of triclosan/m-cresol,reaction temperature and humic acid?HA?on the removal of triclosan/m-cresol and the reusability of BiPO₄ in different systems were investigated.The effect of electrolyte effect on the removal of triclosan/m-cresol was studied,and the type of dominant radicals in the system was determined by free radical trapping experiments.The feasibility of in situ photochemistry activated sulfate in actual water was explored.The conclusions are as follows:?1?Studies on the degradation of triclosan by in situ photochemistry activated sulfate:When pH=7,the degradation rate of triclosan showed a trend of increasing first and then decreasing with the increase of BiPO₄ dosage and SO₄^2-concentration.The higher the initial concentration of triclosan,the worse the removal effect of the reaction system.The degradation rate of triclosan slowly increases with increasing temperature.From the economical point of view,25? is selected as the reaction temperature.The optimum conditions for the degradation of triclosan by in situ photochemistry activated sulfate under pH=7:temperature is 25?,BiPO₄ dosage of 0.5 g/L,Na₂SO₄ concentration of 3 mmol/L,reaction time of 60 min.Under this condition,the 5 mg/L triclosan degradation rate was 97%.1 mg/L humic acid?HA?promoted the degradation of triclosan,but5-10 mg/L HA inhibited the degradation of triclosan.The electrolyte effect indicates that sulfate has a higher promoting effect on the removal of triclosan,nitrate has little effect on the removal of triclosan,but carbonate has a greater degree of inhibition on the removal of triclosan.The degradation rate of triclosan can be maintained at 74%after repeated use of BiPO₄ five times.Free radical trap experiments show that the dominant free radicals in this system are hydroxyl radicals?·OH?and sulfate radicals?·SO₄^-?.The TOC degradation rate of in situ photochemistry activated sulfate to degrade the triclosan was 75.6%.When pH=10,the effects of BiPO₄ dosage and SO₄^2-concentration were the same as pH=7.The optimum conditions for the degradation of triclosan by in situ photochemistry activated sulfate under pH=10:temperature is 25?,BiPO₄dosage of 0.3 g/L,Na₂SO₄ concentration of 4 mmol/L,reaction time is 60 min.Under this condition,the 5 mg/L triclosan degradation rate was 95%.HA has an inhibitory effect on the removal of triclosan,and the higher the concentration of HA,the more obvious the inhibitory effect.Experiments with electrolyte effects showed that the effects of the three anions were the same as pH=7.Free radical trap experiments show that the dominant free radicals in this system are hydroxyl radicals?·OH?and sulfate radicals?·SO₄^-?.The TOC of of in situ photochemistry activated sulfate to degrade the triclosan was 66.2%.The removal of m-cresol by in situ photochemistry activated sulfate showed that the degradation rate of m-cresol showed a trend of increasing first and then decreasing with the increase of BiPO₄ dosage and SO₄^2-concentration.The m-cresol degradation rate is higher under neutral conditions than under acidic or alkaline conditions.The m-cresol degradation rate decreases as the initial concentration increases.The effect of temperature on the degradation of m-cresol is consistent with the effect on the degradation of triclosan.The optimum conditions for the degradation of m-cresol by in situ photochemistry activated sulfate were as follows:temperature is 25?,BiPO₄ dosage of 0.5 g/L,Na₂SO₄concentration of 3 mmol/L,pH=7,and the reaction time of 60 min.Under this condition,the degradation rate of 10 mg/L m-cresol was 92%.1 mg/L HA has a certain promoting effect on the degradation of m-cresol,but 5-10 mg/L HA has a greater inhibitory effect on the degradation of m-cresol.Sulfate has a higher promoting effect on the removal of triclosan,nitrate has little effect on the removal of m-cresol.However,the presence of carbonate has a greater degree of inhibition of the removal of m-cresol.After repeated use of BiPO₄ five times,the degradation rate of m-cresol can be maintained at 70%.Free radical trapping experiments show that the dominant free radical in the system is·OH and·SO₄^-,which promotes the degradation of m-cresol to some extent.The degradation rate of TOC in the m-cresol system by in situ photochemistry activated sulfate was55%.?3?The application of in situ photochemistry activated sulfate in actual water shows that:When conditions are:25?,BiPO₄ dosage of 0.5 g/L,Sulfate content in secondary effluent is 1.9 mmol/L,no pH control,the comparative experiments of primary secondary effluent and secondary effluent supplemented with SO₄^2-3mmol/L were carried out.The results showed that the TOC removal rate of secondary effluent supplemented with SO₄^2-was 68%,higher than that of primary secondary effluent?51%?.Mixing triclosan/m-cresol with secondary effluent as actual sewageand,which are treated by in situ photochemistry activated sulfate.When conditions are:25?,BiPO₄ dosage of 0.5 g/L,Sulfate content in secondary effluent is 1.9mmol/L,no pH control,the initial concentrations of triclosan and m-cresol are 5mg/L and 10 mg/L,comparisons were made between non-supplementation of SO₄^2-and supplementation of SO₄^2-to 3 mmol/L.The results show that the degradation rates of triclosan/m-cresol in the system supplemented with SO₄^2-were 80%and 73%respectively,which were 10%and 8%higher than non-supplementation of SO₄^2-.